Back Room Front Room 2

302 ENTERPRISE INFORMATION SYSTEMS VI
based on established psychological studies, as well
as empirical analysis of actual video footage from
human-computer interaction sessions and human-tohuman
dialogues. The results of the synthesis process
can then be applied to avatars, so as to convey
the communicated messages more vividly than plain
textual information or simply to make interaction
more lifelike.
2 MPEG-4 REPRESENTATION
In the framework of MPEG-4 standard, parameters
have been specified for Face and Body Animation
(FBA) by defining specific Face and Body nodes in
the scene graph. The goal of FBA definition is the
animation of both realistic and cartoonist characters.
Thus, MPEG-4 has defined a large set of parameters
and the user can select subsets of these parameters
according to the application, especially for the body,
for which the animation is much more complex. The
FBA part can be also combined with multimodal
input (e.g. linguistic and paralinguistic speech analysis).
2.1 Facial Animation
MPEG-4 specifies 84 feature points on the neutral
face, which provide spatial reference for FAPs definition.
The FAP set contains two high-level parameters,
visemes and expressions. In particular, the Facial
Definition Parameter (FDP) and the Facial Animation
Parameter (FAP) set were designed in the
MPEG-4 framework to allow the definition of a facial
shape and texture, eliminating the need for
specifying the topology of the underlying geometry,
through FDPs, and the animation of faces reproducing
expressions, emotions and speech pronunciation,
through FAPs. By monitoring facial gestures corresponding
to FDP and/or FAP movements over time,
it is possible to derive cues about user’s expressions
and emotions. Various results have been presented
regarding classification of archetypal expressions of
faces, mainly based on features or points mainly
extracted from the mouth and eyes areas of the
faces. These results indicate that facial expressions,
possibly combined with gestures and speech, when
the latter is available, provide cues that can be used
to perceive a person’s emotional state.
The second version of the standard, following
the same procedure with the facial definition and
animation (through FDPs and FAPs), describes the
anatomy of the human body with groups of distinct
tokens, eliminating the need to specify the topology
of the underlying geometry. These tokens can then
be mapped to automatically detected measurements
and indications of motion on a video sequence, thus,
they can help to estimate a real motion conveyed by
the subject and, if required, approximate it by means
of a synthetic one.
2.2 Body Animation
In general, an MPEG body is a collection of
nodes. The Body Definition Parameter (BDP) set
provides information about body surface, body
dimensions and texture, while Body Animation
Parameters (BAPs) transform the posture of the
body. BAPs describe the topology of the human
skeleton, taking into consideration joints’ limitations
and independent degrees of freedom in the
skeleton model of the different body parts.
2.2.1 BBA (Bone Based Animation)
The MPEG-4 BBA offers a standardized interchange
format extending the MPEG-4 FBA (Preda &
Preteux, 2002). In BBA the skeleton is a hierarchical
structure made of bones. In this hierarchy every
bone has one parent and can have as children other
bones, muscles or 3D objects. For the movement of
every bone we have to define the influence of this
movement to the skin of our model, the movement
of its children and the related inverse kinematics.
3 EMOTION REPRESENTATION
The obvious goal for emotion analysis applications
is to assign category labels that identify emotional
states. However, labels as such are very poor descriptions,
especially since humans use a daunting
number of labels to describe emotion. Therefore we
need to incorporate a more transparent, as well as
continuous representation, that matches closely our
conception of what emotions are or, at least, how
they are expressed and perceived.
Activation-emotion space (Whissel, 1989) is a
representation that is both simple and capable of
capturing a wide range of significant issues in emotion.
It rests on a simplified treatment of two key
themes:
�� Valence: The clearest common element of emotional
states is that the person is materially influenced
by feelings that are ‘valenced’, i.e.
they are centrally concerned with positive or
negative evaluations of people or things or
events. The link between emotion and valencing
is widely agreed
�� Activation level: Research has recognised that
emotional states involve dispositions to act in
certain ways. A basic way of reflecting that